As described in the design, the maintenance daemon will only start
a new round once all jobs from the old round are finished. Add this
functionality now. As the list of jobs of the current round is also
relevant information, we expose it over HTTP. In order to do so, we
keep an in-memory copy of the job list (while the authoritative copy
is still kept in the configuration, as per our design).

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>